In some respects, the bundling of Flash contradicted earlier Microsoft statements that it would not allow plug-ins for IE10 on Metro, including Flash Player, in either Windows 8 or its ARM-based offshoot, Windows RT. Many Windows observers, however, gave Microsoft a pass because Flash was technically not a plug-in, but was instead baked into IE10's code.

Last September, when he announced IE10 on Metro would be plug-in free, Dean Hachamovitch, the company's lead executive for the browser, made this argument: "Running Metro style IE plug-in free improves battery life as well as security, reliability, and privacy for consumers."

Four days ago, Hachamovitch didn't mention last year's promise other than to repeat that IE10 on Metro will be free of plug-ins. "The Metro style browser continues to provide no support for other separate ActiveX controls or plug-ins," said Hachamovitch.

Microsoft has developed two versions of IE10 for Windows 8. One will run in the Metro interface, the tile-based look borrowed from Windows Phone, while the other will run on the more traditional desktop. Because both rely on the same rendering engine -- the core code -- both utilize the integrated Flash Player.

Computerworld confirmed that by pointing IE10 on both the desktop and in Metro to the Flash Player version-checking page: Each flavor of IE10 returned the same results: 11.3.370.178, a slightly-newer version than what Adobe has shipped to other browsers.

That means users of IE10 on Windows 8's desktop do not need to download and install the usual ActivX-based Flash Player plug-in for older versions of the OS, including XP, Vista and Windows 7.

Al Hilwa, an analyst with IDC, said embedding Flash could give Microsoft an advantage.

"Integrating Flash into Metro IE[10] is a ... smart move for Microsoft as it will help them set Windows 8 and Windows RT tablets apart from the iPad," argued Hilwa in an email. "In fact, with Flash and bundled Office apps, Windows RT becomes much more viable [than] in the early days when the app portfolio was still forming."

Hachamovitch drew some of the same conclusions, but as is Microsoft's practice, didn't name either its tablet-making rival's name or the tablet itself.

"Metro style IE10 with Flash on Windows 8 enables people to see more of the Web working with high quality, especially compared with the experience in other touch-first or tablet experiences," Hachamovitch said, clearly referring to the iPad.

Metro IE10 on Windows 8 Release Preview has Flash Player baked in, as a check with Adobe verifies.

But the integration of Flash with IE10 won't give an edge over only Apple. Rival browsers may also be out in the cold.

Adobe has not said whether it will work with other browser makers -- Google and Mozilla in particular -- in the same fashion to integrate Flash Player with their applications on Metro. Google may have a leg up: It's bundled Flash Player with Chrome for two years.

Adobe did not respond to questions today about how it will work with Google and Mozilla, or whether it will.

And neither Google or Mozilla immediately replied to questions about how they plan to compete with the Flash-equipped IE10. Both firms have pledged to come up with Metro versions of their Chrome and Firefox browsers, and last month each had dunned their rival's decision to bar all but IE10 access to Win32 APIs (application programming interfaces) from within Metro.

Because Microsoft has baked Flash Player into IE10, it will also use its own Windows Update service to provide security and feature updates to Adobe's software. Previously, Chrome was the only browser that included Flash Player updates with its browser.

"By updating Flash through Windows Update, like IE, we make security more convenient for customers," said Hachamovitch.

But not all websites with Flash will be viewable using IE10 on Metro, Hachamovitch warned: Only those sites that Microsoft adds to IE's Compatibility View (CV) list -- a whitelist that debuted in 2011 with IE8, designed to allow URLs to render as if they were viewed by an older version of the browser -- will show Flash in Metro's IE10.

"We place sites with Flash content on the CV list if doing so delivers the best user experience in Metro style IE with those sites," said Hachamovitch, who promised that information on how site developers could petition for inclusion on the list would be released at some later date.